You might wonder why such difference exists between control and value directives. Well, This is due to:

Backward compatibility, I wanted users to be able to upgrade to v2 without having to revisit their CSS files, they only need to change RTLCSS configuration.So, In order to support the “Replace” directive /*rtl:{value}*/, all directives names need to be known in advance.

PostCSS does not treat CSS comments found inside delcaration values as nodes.